This invention relates to the generation of product gases.
More particularly, the invention relates to the production of H.sub.2 and CO-containing gases.
Still more specifically, the invention relates to the production of gases of the kind mentioned above, from particulate solid fuels such as coal or coke.
The basic concept of making such gases is already known. The purpose is to convert coal or coke into a product gas which can be further employed in a multitude of applications, for example as a source of chemicals, as a reduction gas or as a substitute for increasingly scarce natural gas. The main problem encountered in the production of such gases is the supply of the heat required in order to effect gasification of the coal or coke with such known gasifying agent as steam (water vapor).
Proposals have been made in the prior art for effecting steam gasification of coal in a fixed-bed reactor, in a fluidized-bed reactor or in suspension (i.e., in cloud form). The required heat is supplied in these processes either autothermically (reaction heat is produced in the gas generator by partial combustion of the coal by adding certain quantities of oxygen to the steam used as a gasification agent) or allothermically (heat is produced externally of the gas generator by combusting coal or other fuel and is introduced into the gas generator via a heat carrier, e.g., partially combusted coal particles or ceramic bodies). The autothermic method requires, as mentioned above, the addition of oxygen. This is a draw-back for many applications since it means that pure oxygen must be produced in a special installation and must then be mixed with the steam, since air cannot be used in place of oxygen because its nitrogen content would undesirably influence the resulting product gas composition.
Also known from the prior art is a process of steam-gasification using superheated steam as heat-carrier. However, due to the low specific heat of steam even high-level superheating--e.g., in excess of 1100.degree. C.--results only in gasification at relatively low temperatures. Therefore, this process is suitable only for highly-reactive coal, such as lignite. Also, it requires the use of substantially greater quantities of steam (for heating) than is needed for the actual gasification reaction. In addition, the steam generator and the condensers must be much more elaborate (and hence expensive) than would be required for the gasification process per se.